Downloading extra user-created levels
(see note)
In fullscreen mode, some visual artifacts follow the mouse.
When switching from fullscreen to windowed mode, the screen size
changes but the window still takes up the whole screen; starting in
windowed mode works ok.
In windowed mode, the program does not grab the mouse when playing a game.

The in-game system for downloading level sets doesn't seem to work in Wine; they can instead be downloaded from this page. Downloaded level sets go in ~/.wine/drive_c/Program Files/Ricochet Infinity/Rounds.

If you get an exe file or a message telling you to download levels from within the game, you need to scroll down and change the download format to "raw files".
The exe installers are designed for Ricochet Lost Worlds and won't install the levels for Ricochet Infinity.